Redmond has confirmed that like its predecessor, Windows 7 can be used for up to 120 days without providing a product activation key.

Redmond has confirmed that like its predecessor, Windows 7 can be used for up to 120 days without providing a product activation key.

Although Microsoft generally touts a 30-day time limit for users to activate their copies of the company's operating system, a little-known command designed for corporate administrators can be used by anyone to "reset" the countdown up to three times.

This week the Windows Secrets newsletter published step-by-step instructions on using a single-line command to add an additional 90 days to the stock 30-day grace period.

Microsoft allows users to install and run any version of Windows 7 for up to 30 days without requiring a product activation key, a 25-character alphanumeric string that proves the copy is legitimate. During the 30-day grace period, Windows 7 operates as if it has been activated. As the grace period shrinks, however, increasingly-frequent messages appear on the screen. For example, on days four through 27, a pop-up asks the user to activate once each day. During days 28 and 29, the pop-up displays every four hours, while on Day 30, it appears hourly.

But by invoking the "slmgr -rearm" command at a Windows 7 command prompt, users can reset the time-until-activation to 30 days, said Woody Leonard, a contributing editor to Windows Secrets and the author of several computer books, including Windows Vista All-in-One Desk Reference for Dummies.

"You can run the -rearm trick a total of three times," said Leonard. "If you perform a -rearm at the end of each 30-day period, you end up with 120 days of full, unfettered Windows 7 use, without having to supply an activation key."

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Leonard tested the command on Windows 7 RTM (release to manufacturing), the final build of the operating system that Microsoft has already shipped to computer makers and distributed to IT professionals and developers who subscribe to the TechNet and MSDN services.

Microsoft confirmed that "-rearm" can be used as many as three times by Windows 7 users to avoid activation. "This means [that] a total of 120 days total time is available as a grace period to customers that take advantage of -rearm," said a company spokeswoman.

Nor is extending the grace period a violation of the Windows 7 End User License Agreement (EULA), the spokeswoman said.

Windows Secrets and others published information about the same grace period extension two years ago, shortly after Microsoft launched Vista. "Rearm is the same in Windows 7 as in Vista," noted Brian Livingston, the editor of Windows Secrets, in an interview.

Microsoft introduced product activation in 2001's Office XP and also used it in that year's Windows XP. The feature was toughened up for Vista, however; after the grace period, non-activated PCs running Vista dropped into what Microsoft called "reduced functionality" mode. In reduced mode, users could only browse the Web with Internet Explorer, and then only for an hour before being forced to again log on.

In early 2008, however, Microsoft revamped that process, which some had dubbed a "kill switch," in favor of a black background and constant nagging reminders. Later in 2008, Microsoft introduced the same procedures to Windows XP when it rolled out Service Pack 3 (SP3).

In February 2009, Microsoft said Windows 7 would use the same reminders, a black screen and persistent notices.